Authorities investigating the Las Vegas massacre turned Wednesday to the shooter’s girlfriend, hoping for more answers about the gunman and what may have sparked the deadliest mass shooting in modern U.S. history.

Investigators have spent the days since Sunday’s attack — which killed 58 people and injured hundreds more — struggling to explain why 64-year-old Stephen Paddock holed up in a high-rise hotel overlooking the Las Vegas Strip and opened fire on concertgoers at a country music festival far below.

What they have found so far has been chilling evidence of extensive preparations, as Paddock turned his two-room suite in the Mandalay Bay Resort and Casino into an armed fortress. He brought in 23 guns along with “bump” stocks that can allow them to more quickly fire bullets, police said. The gunman also placed cameras so that he could monitor the arrival of police officers, who eventually breached his room and found that he killed himself before they arrived.

But a motive has remained elusive. Police hoped they could learn more from Paddock’s girlfriend, Marilou Danley, who was in the Philippines when the shooting occurred.

Danley arrived late Tuesday night at Los Angeles International Airport and was met by FBI agents, according to a person familiar with the investigation. She is considered a critical witness in trying to decipher Paddock’s motive.

While investigators have described her as a “person of interest,” they have not suggested that she is considered an accomplice or involved in any way.

FBI agents speaking to Danley have essentially two critical questions: Did she have any idea what motivated him, and did she have any knowledge of what was about to take place and not alert authorities? Such was the case for Noor Salman, the wife of the Orlando gunman who killed 49 people last year. Salman was later arrested and charged with aiding and abetting terrorism and obstructing justice.

There were no immediate, obvious indications that Danley would fit the same bill, a person familiar with the case said, though they stressed that the investigation was still early. Investigators still have to run down any potential leads Danley may provide.

Given how little has emerged in Paddock’s past that could foreshadow the attack, the “best lead is through this girlfriend,” said Sen. Dean Heller (R-Nev.).

“They don’t know a lot about who the girlfriend is and why she left the country a week prior to the shooting,” said Heller, who has been briefed by authorities. “She is someone they need to have this discussion with to better under­stand the shooting and what his thought process was.”

FBI Deputy Director Andrew McCabe said Wednesday morning that he is surprised they have not found evidence pointing to the gunman’s motive yet.

“There’s all kinds of things that surprise us in each one of these events,” McCabe told CNBC. “This individual and this attack didn’t leave the sort of immediately accessible thumbprints that you find on some mass casualty attacks….We look for actual indicators of affiliation, of motive, of intent, and so far we’re not there. We don’t have those sort of indicators.”

McCabe said agents have been reconstructing “the life, the behavior, the pattern of activity of this individual and anyone and everyone who may have crossed his path in the days and the weeks leading up to this horrific event.”

He said so far investigators have not had any problems accessing the gunman’s computer electronic devices.

Amid a backdrop of anguish and questions, President Trump on Wednesday headed to Las Vegas to address law enforcement officials in Las Vegas as well as survivors of Sunday’s massacre.

“We’re going to pay our respects and see the police who really have done a fantastic job,” Trump said to reporters before he left Washington for Nevada. “It’s a very, very sad day for me, personally.”

Piece by piece, investigators have put together a profile of Paddock — a retired accountant — making meticulous preparations for the moment when he smashed a plate-glass window in the 32nd floor of his hotel room and opened fire with a weapon, apparently modified to spew bullets with the split-second speed of an automatic rifle.

As he fired round after round during an 11-minute stretch from a suite at the Mandalay Bay, Paddock used multiple video cameras to keep an eye out for police storming his hotel room, according to Clark County Sheriff Joe Lombardo.

“It was preplanned, extensively, and I’m pretty sure that he evaluated everything that he did in his actions, which is troublesome,” Lombardo said Tuesday.

Paddock hid one camera in the peephole of his suite and two more in the hall, at least one of them disguised on a service cart, authorities said. At one point, he shot numerous rounds through the door, wounding a security guard.

Paddock eventually put a gun in his own mouth and pulled the trigger as SWAT officers closed in. They found him with blood pooling behind his head and around the empty shell casings that littered the carpet, a handgun near his body.

Once police entered the suite, they found that Paddock had brought 23 guns inside since he checked into the hotel on Thursday. Police also found another 26 guns at two other properties in Nevada and a large collection of ammunition and a chemical that can be used to make bombs.

Many of Paddock’s guns were purchased in recent years. Between October 2016 and Sept. 28, the day Paddock checked into the Mandalay Bay, Paddock bought 33 guns, the “majority of them rifles,” Jill A. Snyder, the special agent in charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives in San Francisco, said Wednesday in an interview with “CBS This Morning.”

Paddock also had substantial ammunition in the room, with clips containing between 60 and 100 rounds, Snyder said. During a news briefing a day earlier, Snyder said Paddock had purchased shotguns, handguns and rifles in Nevada, Utah, California and Texas. She also said that inside Paddock’s suite, authorities found a dozen “bump” stocks that can enable guns to fire bullets at a more rapid clip.

Included in the cache of guns found in his room: An AR-15-type rifle with a high-capacity magazine, another AR-15-type rifle with a magnification scope commonly used for hunting and a bipod stand to help steady it, according to law enforcement officials and experts who reviewed images of the weapons posted online.

Until carrying out the massacre Sunday night, Paddock had no criminal history himself. Despite repeated claims by the Islamic State to the contrary, he also had no ties to international terrorism groups, authorities said. He had done some government work, spent three years working for a defense contractor and had twice been divorced. Paddock was known to gamble routinely and extensively.

Some public officials seemed to suggest Paddock’s mind was troubled, though there were no immediate indications that he had been diagnosed with a mental illness or was anything other than fully aware of what he was doing.

“A normal person would not cause this type of harm to innocent people,” said Rep. Ruben Kihuen (D-Nev.). “Clearly, there was something wrong with this man.”

Neighbors in several states where Paddock owned homes in retirement communities described him as surly, unfriendly and standoffish. Paddock was the son of a bank robber who was once on the FBI’s most-wanted list and whom authorities described at the time as a “psychopath,” but Paddock’s brother said their father was not involved in their lives when they were children.

Relatives say the roots of Paddock’s loner lifestyle might have been planted on July 28, 1960. On that day, when Paddock was 7, a neighbor from across the street took him swimming. The neighbor told a local newspaper at the time that she knew authorities were coming for his father, and she wanted to spare the young boy from the trauma of seeing his father taken away. From that point on, Paddock’s family was never the same.

People close to the investigation also said that in the weeks before the attack, Paddock transferred a large amount of money — close to $100,000 — to someone in the Philippines, possibly his girlfriend. The significance of that development was not immediately clear, though investigators said they were interested in probing Paddock’s finances and his avid interest in high-stakes gambling.

Danley’s sister, interviewed by Australia’s Channel 7, suggested that Paddock had arranged Danley’s trip to visit her homeland to keep her from undermining the attack plans.

“I know she doesn’t know anything as well like us,” said the sister, whose identity was shielded by the channel. “She was sent away. She was away so that she would not be there to interfere with what he’s planning.”

According to court records, Danley appears to have been living with Paddock as early as August 2013, while she was still married to another man, named Geary Danley. Geary and Marilou Danley were married in Las Vegas in 1990. According to court records, they jointly filed for divorce on Feb. 25, 2015, and the divorce was finalized the next day.

At his home in Orlando, Eric Paddock, Stephen Paddock’s brother, said he also doubts Danley had any prior knowledge of the incident and speculated that Stephen might have been trying to quietly ensure her financial security. Stephen Paddock loved and doted on his girlfriend, whom he had met when she was a hostess at a casino, Eric Paddock said. The couple often gambled side by side.

“He manipulated her to be as far away from here and safe when he committed this,” Eric Paddock said. “The people he loved he took care of, and as he was descending into hell he took care of her.”

Coroner John Fudenberg on Tuesday evening clarified that Paddock was among the 59 counted as slain; previously, authorities had said he wasn’t. More than 500 people were wounded in the attack or injured in the rush to flee.

Undersheriff Kevin C. Mc­Mahill, speaking after Fudenberg at a news briefing, warned that the number of dead and injured could fluctuate as the investigation progresses.

Hospitals across the region continued to treat patients from the scene, many of them seriously injured. Sunrise Hospital and Medical Center said that as of Tuesday, it had 59 patients from the rampage, 31 of them still in critical condition. University Medical Center said it had 64 patients from the attack, 12 of them critical.